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fscache: Provide and use cache methods to lookup/create/free a volume

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Add cache methods to lookup, create and remove a volume.

Looking up or creating the volume requires the cache pinning for access;
freeing the volume requires the volume pinning for access.  The
->acquire_volume() method is used to ask the cache backend to lookup and,
if necessary, create a volume; the ->free_volume() method is used to free
the resources for a volume.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819597821.215744.5225318658134989949.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906898645.143852.8537799955945956818.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967099771.1823006.1455197910571061835.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021507345.640689.4073511598838843040.stgit@warthog.procyon.org.uk/ # v4
This commit is contained in:
David Howells 2021-10-20 15:26:17 +01:00
parent 2e0c76aee2
commit bfa22da3ed
3 changed files with 103 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

89
fs/fscache/volume.c
View File

@ -15,6 +15,8 @@ static struct hlist_bl_head fscache_volume_hash[1 << fscache_volume_hash_shift];
static atomic_t fscache_volume_debug_id;
static LIST_HEAD(fscache_volumes);
static void fscache_create_volume_work(struct work_struct *work);
struct fscache_volume *fscache_get_volume(struct fscache_volume *volume,
enum fscache_volume_trace where)
{
@ -213,7 +215,7 @@ static struct fscache_volume *fscache_alloc_volume(const char *volume_key,
volume->cache = cache;
INIT_LIST_HEAD(&volume->proc_link);
INIT_WORK(&volume->work, NULL /* PLACEHOLDER */);
INIT_WORK(&volume->work, fscache_create_volume_work);
refcount_set(&volume->ref, 1);
spin_lock_init(&volume->lock);
@ -249,6 +251,58 @@ err_cache:
return NULL;
}
/*
* Create a volume's representation on disk. Have a volume ref and a cache
* access we have to release.
*/
static void fscache_create_volume_work(struct work_struct *work)
{
const struct fscache_cache_ops *ops;
struct fscache_volume *volume =
container_of(work, struct fscache_volume, work);
fscache_see_volume(volume, fscache_volume_see_create_work);
ops = volume->cache->ops;
if (ops->acquire_volume)
ops->acquire_volume(volume);
fscache_end_cache_access(volume->cache,
fscache_access_acquire_volume_end);
clear_bit_unlock(FSCACHE_VOLUME_CREATING, &volume->flags);
wake_up_bit(&volume->flags, FSCACHE_VOLUME_CREATING);
fscache_put_volume(volume, fscache_volume_put_create_work);
}
/*
* Dispatch a worker thread to create a volume's representation on disk.
*/
void fscache_create_volume(struct fscache_volume *volume, bool wait)
{
if (test_and_set_bit(FSCACHE_VOLUME_CREATING, &volume->flags))
goto maybe_wait;
if (volume->cache_priv)
goto no_wait; /* We raced */
if (!fscache_begin_cache_access(volume->cache,
fscache_access_acquire_volume))
goto no_wait;
fscache_get_volume(volume, fscache_volume_get_create_work);
if (!schedule_work(&volume->work))
fscache_put_volume(volume, fscache_volume_put_create_work);
maybe_wait:
if (wait) {
fscache_see_volume(volume, fscache_volume_wait_create_work);
wait_on_bit(&volume->flags, FSCACHE_VOLUME_CREATING,
TASK_UNINTERRUPTIBLE);
}
return;
no_wait:
clear_bit_unlock(FSCACHE_VOLUME_CREATING, &volume->flags);
wake_up_bit(&volume->flags, FSCACHE_VOLUME_CREATING);
}
/*
* Acquire a volume representation cookie and link it to a (proposed) cache.
*/
@ -269,7 +323,7 @@ struct fscache_volume *__fscache_acquire_volume(const char *volume_key,
return ERR_PTR(-EBUSY);
}
// PLACEHOLDER: Create the volume if we have a cache available
fscache_create_volume(volume, false);
return volume;
}
EXPORT_SYMBOL(__fscache_acquire_volume);
@ -316,7 +370,12 @@ static void fscache_free_volume(struct fscache_volume *volume)
struct fscache_cache *cache = volume->cache;
if (volume->cache_priv) {
// PLACEHOLDER: Detach any attached cache
__fscache_begin_volume_access(volume, NULL,
fscache_access_relinquish_volume);
if (volume->cache_priv)
cache->ops->free_volume(volume);
fscache_end_volume_access(volume, NULL,
fscache_access_relinquish_volume_end);
}
down_write(&fscache_addremove_sem);
@ -369,6 +428,30 @@ void __fscache_relinquish_volume(struct fscache_volume *volume,
}
EXPORT_SYMBOL(__fscache_relinquish_volume);
/**
* fscache_withdraw_volume - Withdraw a volume from being cached
* @volume: Volume cookie
*
* Withdraw a cache volume from service, waiting for all accesses to complete
* before returning.
*/
void fscache_withdraw_volume(struct fscache_volume *volume)
{
int n_accesses;
_debug("withdraw V=%x", volume->debug_id);
/* Allow wakeups on dec-to-0 */
n_accesses = atomic_dec_return(&volume->n_accesses);
trace_fscache_access_volume(volume->debug_id, 0,
refcount_read(&volume->ref),
n_accesses, fscache_access_cache_unpin);
wait_var_event(&volume->n_accesses,
atomic_read(&volume->n_accesses) == 0);
}
EXPORT_SYMBOL(fscache_withdraw_volume);
#ifdef CONFIG_PROC_FS
/*
* Generate a list of volumes in /proc/fs/fscache/volumes

7
include/linux/fscache-cache.h
View File

@ -51,6 +51,12 @@ struct fscache_cache {
struct fscache_cache_ops {
/* name of cache provider */
const char *name;
/* Acquire a volume */
void (*acquire_volume)(struct fscache_volume *volume);
/* Free the cache's data attached to a volume */
void (*free_volume)(struct fscache_volume *volume);
};
extern struct workqueue_struct *fscache_wq;
@ -65,6 +71,7 @@ extern int fscache_add_cache(struct fscache_cache *cache,
const struct fscache_cache_ops *ops,
void *cache_priv);
extern void fscache_withdraw_cache(struct fscache_cache *cache);
extern void fscache_withdraw_volume(struct fscache_volume *volume);
extern void fscache_end_volume_access(struct fscache_volume *volume,
struct fscache_cookie *cookie,

11
include/trace/events/fscache.h
View File

@ -64,8 +64,12 @@ enum fscache_cookie_trace {
};
enum fscache_access_trace {
fscache_access_acquire_volume,
fscache_access_acquire_volume_end,
fscache_access_cache_pin,
fscache_access_cache_unpin,
fscache_access_relinquish_volume,
fscache_access_relinquish_volume_end,
fscache_access_unlive,
};
@ -96,7 +100,8 @@ enum fscache_access_trace {
EM(fscache_volume_put_hash_collision, "PUT hcoll") \
EM(fscache_volume_put_relinquish, "PUT relnq") \
EM(fscache_volume_see_create_work, "SEE creat") \
E_(fscache_volume_see_hash_wake, "SEE hwake")
EM(fscache_volume_see_hash_wake, "SEE hwake") \
E_(fscache_volume_wait_create_work, "WAIT crea")
#define fscache_cookie_traces \
EM(fscache_cookie_collision, "*COLLIDE*") \
@ -115,8 +120,12 @@ enum fscache_access_trace {
E_(fscache_cookie_see_work, "- work ")
#define fscache_access_traces \
EM(fscache_access_acquire_volume, "BEGIN acq_vol") \
EM(fscache_access_acquire_volume_end, "END acq_vol") \
EM(fscache_access_cache_pin, "PIN cache ") \
EM(fscache_access_cache_unpin, "UNPIN cache ") \
EM(fscache_access_relinquish_volume, "BEGIN rlq_vol") \
EM(fscache_access_relinquish_volume_end,"END rlq_vol") \
E_(fscache_access_unlive, "END unlive ")
/*